The present invention relates to a control device for a power steering apparatus.
A steering force in a vehicle normally decreases when the vehicle speed increases. In a conventional power steering apparatus for giving an auxiliary power corresponding to the steering force, if a small steering force is set at a low vehicle speed, a steering force required at a high vehicle speed is undesirably too small to drive safely at the high speed. Various conventional devices have proposed to decrease a ratio of auxiliary power input to output in response to an increase in vehicle speed. These devices aim at requiring a sufficiently small steering force at the low vehicle speed but not a small steering force at the high vehicle speed.
It is desirable to increase the steering force when the steering angle is increased with respect to the neutral position thereof. It is preferable to increase the steering force when the angle of the steering wheel turned by a driver is increased. This effect is typically preferred during high-speed driving. However, in a conventional power steering apparatus, an increase in steering force upon turning of the steering wheel is small. Strong demand has arisen for improving steering force control from the viewpoint of safety and steering feeling. In particular, the small increase in steering force during high-speed driving upon turning of the steering wheel leads to excess turning and hence a traffic accident. In order to avoid such danger, large steering forces are preset at both high and low vehicle speeds in some conventional power steering control devices. However, the large steering force leads to uncomfortable feeling during continuous steering with small steering angles. High-speed cruising therefore causes easy tiredness of drivers.